What is being tested?The test measures the amount of thyroid-stimulating hormone (TSH) in your blood, which is an indicator of
thyroid disease. TSH is made by the pituitary gland, a tiny organ located below the brain and behind the sinus cavities. It is part of the body’s
feedback system to maintain stable amounts of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) in the blood.
Thyroid hormones help control the rate at which the body uses energy. When concentrations decrease in the blood, the hypothalamus (an organ in the brain) releases thyrotropin releasing hormone (TRH). This stimulates the release of TSH by the pituitary gland. The TSH in turn stimulates the production and release of T4 and T3 by the thyroid gland, a small butterfly-shaped gland that lies in the neck flat against the windpipe. When all three organs are functioning normally, thyroid hormone levels in the blood remain constant.
